Honeywell Hydranal Manual

HYDRANAL
MANUAL
FOR KARL
FISCHER
TITRATION

This HYDRANAL™ Manual is intended to be a useful
reference handbook for analysts per forming routine
Karl Fischer (KF) titration. It contains practical
recommendations and is the culmination of over
40 years of diligent product development and close
collaboration with our customers. We have tried to
organize the information systematically according
to product groups and application areas to make it
both informative and easy to use.
Besides this handbook, we have also published
many results in the literature and listed them in
the Literature Appendix. For analysts wanting
a deeper understanding of KF principles, we
highly recommend the textbook by Eugen Scholz
“Karl-Fischer Titration” [1].
Over the years, we have investigated the KF titration
of many diverse products and substances. Details
of each particular case are beyond the scope of this
manual, but are available in our comprehensive
Laboratory Reports library. Available Laboratory
Reports are noted in the text with the prefix “L” and
are available for download from our website.
We have always adhered to the principle of
recommending only those working methods
and applications that we have tried and verified
ourselves. We never accept nor copy any untested
publications or methods. By using this principle,
we hope to ensure a high level of working safety
and optimum results for you.
We are here to ser ve you, to help you choose and use
the right Hydranal reagents and develop reliable
working methods. Please feel free to contact us.
We look forward to helping you solve your most
routine or challenging KF titration needs.
HYDRANAL™ Hotline
Please, do not hesitate to
contact us at
hydranal@honeywell.com
hydranal-honeywell.com
Global Market
Thomas Wendt
HYDRANAL Center of Excellence
Seelze, Germany
Tel: +49 5137 999 353
Fax: +49 5137 999 698
Global Market
Dr. Roman Neufeld
HYDRANAL Center of Excellence
Seelze, Germany
Tel: +49 5137 999 451
Global Market
Agnieszka Kossakowska
HYDRANAL Technical Specialist
Warsaw, Poland
Tel: +48 512 355 628
APAC
Charlie Zhang
HYDRANAL Application Lab
Shanghai, China
Tel: ++86 21 2894 4715
APAC
Linda Zhang
HYDRANAL Application Lab
Shanghai, China
Tel: ++86 21 2894 4771
HYDRANAL™ Manual
for Karl Fischer Titration

HYDRANAL™ Manual
for Karl Fischer Titration

1. Introduction:
Innovations by Riedel-de Haën
1.1 New bases ................................................ 1
1.2 New reagents .......................................... 1
1.3 Scientific investigations .................... 1
1.4 Patents ....................................................... 2
1.5 Analytical support ................................ 2
2. HYDRANAL reagents
2.1 HYDRANAL-Composite
one-component reagents
for volumetric titrations ..................... 3
2.2 HYDRANAL-Solvent and
HYDRANAL-Titrant two-
component reagents for
volumetric titrations ............................ 4
2.3 HYDRANAL-Coulomat reagents
for coulometric determinations .... 5
2.4 HYDRANAL products for the
determination of water in
aldehydes and ketones ...................... 6
2.5 HYDRANAL water standards .......... 7
2.6 HYDRANAL for back titration ......... 8
2.7 HYDRANAL buffers .............................. 8
2.8 HYDRANAL auxiliary products ...... 8
3. The advantages of HYDRANAL
3.1 Titration speed ....................................... 9
3.2 End point stability ................................ 9
3.3 Accuracy ................................................. 10
4. Chemical fundamentals behind
Karl Fischer titration
4.1 Working medium ............................... 11
4.2 pH .............................................................. 11
5. Standard procedures for KF titrations
5.1 Volumetric titrations using
the one-component reagent
HYDRANAL-Composite .................. 13
5.2 Volumetric titrations using
the two-component reagent
HYDRANAL-Titrant (E) and
HYDRANAL-Solvent (E) .................. 14
5.3 Coulometric titrations with
HYDRANAL-Coulomat
A/AG/E/AG-H/AG-Oven
and HYDRANAL-Coulomat CG ...15
5.4 Coulometry without a
diaphragm ............................................. 18
5.5 Back titrations ..................................... 18
5.6 Standardization of titer .................. 18
5.7 End point indication ........................ 19
6. Laboratory recommendations
6.1 The KF laboratory .............................. 21
6.2 Titration instrumentation .............. 21
6.3 Titration cells ....................................... 21
6.4 Burettes .................................................. 22
6.5 Working medium renewal .............. 22
6.6 End point stability and
instrumentation delay ..................... 23
7. Sample preparation
7.1 Sampling and sample
treatment ............................................... 24
7.2 Sample size ........................................... 24
7.3 Addition of the sample .................... 25
7.4 Pre-dissolution of the sample ..... 26
7.5 Extraction of water from
the sample ............................................27
8. Variants of the KF titration caused by
the matrix
8.1 Addition of alcohols.......................... 28
8.2 Addition of chloroform ....................29
8.3 Addition of formamide ....................30
8.4 Methanol-free working media .... 30
8.5 Neutralization of bases .................. 31
8.6 Neutralization of acids .................... 32
8.7 Titration at low temperature ........ 33
Contents
HYDRANAL Manual Contents

8.8 Titration at elevated
temperature .......................................... 34
8.9 Titration in boiling methanol ....... 34
8.10 The determination of water
in gases ................................................... 35
8.11 The use of ovens ................................ 36
8.12 Titration curves .................................. 38
9. Organic compounds
9.1 Hydrocarbons ...................................... 40
9.2 Halogenated hydrocarbons ......... 41
9.3 Alcohols .................................................. 42
9.4 Phenols ................................................... 42
9.5 Ethers ...................................................... 44
9.6 Aldehydes and ketones ................... 44
9.7 Carboxylic acids, esters and
salts .......................................................... 48
9.8 Compounds containing
nitrogen .................................................. 49
9.9 Compounds containing sulfur.... 51
9.10 Siloxanes, silanols ............................. 52
9.11 Peroxides ............................................... 52
10. Inorganic compounds
10.1 Salts .......................................................... 53
10.2 Acids, oxides and carbonates ...... 54
11. Foods and natural products
11.1 Carbohydrates..................................... 56
11.2 Fats and fatty products .................. 56
11.3 Dairy and proteinaceous
products ................................................. 56
11.4 Vegetable-based products ........... 57
11.5 Chocolates, sweets, toffees .......... 57
11.6 Bakery products, pastas .................58
12. Medicines and cosmetic products ............ 59
13. Technical products
13.1 Mineral oils, crude oils and
related products ................................. 61
13.2 Paints, lacquers, adhesives .......... 62
13.3 Plastics ................................................... 62
13.4 Liquified gases ................................... 63
14. Appendix
14.1 Literature ............................................... 64
14.2 Subject index ....................................... 65
14.3 Reagent index ..................................... 67
HYDRANAL MANUAL Contents

1
Water content plays an important role in many chemical
processes, product performance, organoleptic properties
and stabilit y. A defined, reliable and truly practical method for
water measurement was introduced in 1935 when chemist
Karl Fischer (KF) published his manuscript “New procedure
for the determination of the water content in liquids and
solids.” (K. Fischer; Angew. Chemie 1935, 48, 394). Karl
Fischer titration, as it was to be known, could be followed
by nearly any laboratory interested in water determination.
Consequently, it has become one of the most frequently
employed methods in analy tical chemistr y.
But the technique was open to improvement. Beginning in
1979, Riedel-de Haën chemists Eugen Scholz and Helga
Hof fmann investigated ways to improve Karl Fischer titration,
making it safer, more accurate, easier to use and applicable
to a wider range of substrates. These improvements became
the foundation of the Hydranal™ product line described in
this Manual.
Three impor tant innovations define the Hydranal line:
• Noxious pyridine was replaced by bases that are both
safer and more ef fective.
• New reagents and techniques reduce the number of
required components, make end points clearer and more
stable, and give faster and more sensitive reactions.
• Safet y innovations beyond pyridine replacement include
removal of halogenated hydrocarbons and replacement
of methanol.
The results of Dr. Scholz and his team’s investigations were
of such fundamental impor tance that patents were received
for many of the new reagents and their use. So far, more than
fifty patents have been issued or are pending in Europe, the
US, Japan and other countries. Research continues to this
day toward the development of new, innovative Hydranal
products and working methods.
1.1 New bases
The original KF method and many currently commercially
available products use noxious pyridine as the base.
Beginning in 1979, Riedel-de Haën initiated a series of
systematic investigations led by Dr. Eugen Scholz aimed at
replacing pyridine. The result of these investigations soon
showed that pyridine could be replaced by bases that are
superior for such applications. The most significant results
were published in the Fresenius “Zeitschrift für Analytische
Chemie” in the series entitled “Karl Fischer Reagents without
Pyridine” [2-9]. The initial publications reported on the use
of diethanolamine as a base [2-5]. Subsequent articles [8]
reported on the use of imidazole, which has since proven to
be the best Karl Fischer base. Imidazole, an integral Hydranal
component, proved to be an ideal buf fer for the KF system; it
ensures a rapid and accurate KF titration.
1.2 New reagents
As a result of the investigations undertaken, new reagents
for the determination of water were developed that surpass
the classic Karl Fischer solutions. The first two-component
reagent containing diethanolamine as the base, Hydranal-
Solvent and Hydranal-Titrant, was introduced in 1980. This
reagent allows a rapid titration with a stable end point. The
base of this reagent was changed to imidazole in 1986 to
improve the buffering of the KF system and increase the
water capacity of the solvent to 7 mg/mL. This reagent is
described in detail in section 2.2.
Hydranal-Composite, a one-component reagent that
contains imidazole as the base, was introduced to the market
in 1980. Details of this reagent can to be found in section 2.1.
In later years the coulometric reagents Hydranal-Coulomat
A and Hydranal-Coulomat C followed and enabled the
coulometric technique for water determination (see
section 2.3). In 1991 a new set of coulometric reagents
free of halogenated hydrocarbons was introduced. Next
were introduced special methanol-free reagents for the
determination of water in aldehydes and ketones, designated
Hydranal-K reagents. This product line comprises the
Hydranal-Composite 5 K and Hydranal-Medium K for
the volumetric determination of water and Hydranal-
Coulomat AK , and Hydranal-Coulomat CG-K for coulometric
determination (section 2.4).
The range of KF titration reagents was completed with the
addition of Hydranal-Water Standards (section 2.5), titration
reagents for back titrations and buffering substances
(sections 2.6 and 2.7, respectively), as well as ethanol-based
reagents, the Hydranal-E t ypes.
The most recent developments include Hydranal-CRM
Water Standards and Hydranal-Water Standard 0.1 PC
with improved stability. Research into additional non-toxic
reagents is ongoing.
1.3 Scientific investigations
In conjunction with the development work undertaken,
fundamental questions required satisfactory answers. The
introduction of new reagents demanded the verification
of the stoichiometry of the reaction. We came to the
conclusion that the well known equations for the reaction
did not fully describe the course of the KF reaction obser ved
and necessitated further investigation. The results of the
investigations under taken by Dr. Eugen Scholz and his team
have since been published in both English and German by
Springer Verlag [1].
Chapter 1. Introduction: Innovations by Riedel-de Haën
HYDRANAL Manual Chapter 1: Introduction: Innovations by Riedel-de Haën

2
1. ROH + SO2 + R’N [R’NH]SO3R
2. [R’NH]SO3R + H O + I2 + 2R’N  2[R’NH]I + [R’NH]SO4R
2
ROH = alcohol, t ypically methanol
R’N = base
Figure 1.3. Scheme of Karl Fischer reaction.
The sulfur dioxide reacts with the alcohol to form an ester
that is subsequently neutralized by the base (Figure 1.3). The
anion of the alkyl sulfurous acid is the reactive component
and is already present in the KF reagent. The titration of
water constitutes the oxidation of the alkyl-sulfite anion to
alk yl sulfate by the iodine. This reaction consumes water.
T his means that t wo significant prerequisites must be fulfilled
in order to assure a stoichiometric course of the KF reaction.
The first is the presence of a suitable alcohol to esterify the
sulfur dioxide completely [1]. The practical consequences of
the results are explained in section 4.1.
The second is the presence of a suitable base necessar y for
the complete neutralization of the acids produced during
the reaction. The basicit y of pyridine is too low to completely
neutralize the acid and is the cause of the sluggish titration
observed using the classic (non-Hydranal) KF titration
reagents. If the base is too strong, the solution becomes too
alkaline and an end point will not be reached. A titration in
the pH range of 5-7.5 is preferred and this can be achieved
by the use of imidazole. The pH adjustment is therefore of
prime importance for the course of an efficient KF titration
(see section 4.2).
1.4 Patents
The results of our investigations were of such fundamental
importance that patents were filed for many of the new
Hydranal reagents and their use. More than 50 patents
have been filed, many of which have since been granted
and are, therefore, binding. Of particular note are patents
DP 3008421, EP 0035066, EP 0127740, EP0075246,
EP0135098, GB 2,234,066, JP 61-54182, USP 4,740,471,
USP 4,378,972, USP 4,748,126, USP 4,429,048, USP
4,619,900 and the USP 5,139,955. Additional patents have
been granted in other countries, including Spain, Brazil,
South Africa, etc. Fur ther patents are pending.
It is important to note that Honeywell does not permit
the manufacture of patented reagents for commercial or
personal use. This also applies to the application of such
reagents. The procurement of the patented reagent also
grants the right of its usage.
1.5 Analytical support
The determination of water using the KF method is carried
out using specialized instrumentation. There are a number
of commercially available instruments that are designed
specifically for KF titrations. Our Hydranal reagents are
compatible with these titrators and our well-equipped
Hydranal laboratories have the most important KF
instruments available on the international market.
Often we are asked by customers for technical assistanceto
help them determine the water content of their specific
products. In most cases we were able to find an acceptable
solution to their application. When we deem these methods
to be of general interest, which is of ten the case, we mention
them in this Manual, and sometimes publish a Laboratory
Report on the subject. Available Laboratory Reports are
noted in the text with the prefix “L”. For some samples we
offer also Ph. Eur. Suitability Test Reports which have prefix
"S". Additionally, we publish Technical Information Sheets
(prefix "T") containing useful technical tips on different
KF T related topics. All reports can be downloaded from our
website hydranal-honey well.com.
Take advantage of our vast experience with KF titration
by contacting our Hydranal laboratories for help and
information on:
• KF titration in general
• How to deal with dif ficult samples
• Method development work on your samples,
free of charge
• How to receive detailed application protocols from us
• How to obtain Hydranal product information
Our experts at the Hydranal hotline can be accessed
by phone, fax or e-mail. Contact details are listed at the
beginning of this Manual.
HYDRANAL Manual Chapter 1: Introduction: Innovations by Riedel-de Haën

3
Pyridine-free Karl Fischer reagents produced by Honeywell
are sold under the registered trademark Hydranal. Hydranal
is a result of our dedicated investigations into improving
the safety, accuracy and ease-of-use of the KF technique.
Hydranal reagents fulfill all the requirements of practical
laboratory analysis and enable analysts to choose the
optimum reagent for their specific application and
instrumentation. The Hydranal product line consists of one-
component and two-component reagents for volumetric
determinations, coulometric reagents and special reagents
for the determination of water in ketones and other difficult
substances. The product range is complemented by
calibration standards for the determination of the titer (water
equivalent) and buffer solutions.
The Hydranal range of reagents uses imidazole or
diethanolamine (available in a few reagents) as the base,
rather than pyridine. Imidazole and diethanolamine are
effective and guarantee reliable analyses. The composition
of Hydranal reagents, their target applications and usage
guidelines are summarized in the following sections.
2.1 HYDRANAL-Composite one-component
reagents for volumetric titrations
One-component reagents contain all the reactants (i.e.
iodine, sulfur dioxide and imidazole) dissolved in a suitable
alcohol. These reagents are intended for the volumetric KF
titration of water.
2.1.1 Applications
Hydranal-Composite is a universal reagent for volumetric
KF titration methods of determining water. It is suitable
for all commercially available instrumentation. Hydranal-
Composite one-component reagent is preferred because
it is relatively simple to use. All necessary reactants are
conveniently contained in one solution. The working
medium (i.e. the solvent required) is chosen according
to the dissolution properties of the sample substance
being analyzed.
2.1.2 General procedure
The following procedure (Figure 2.1.2) is recommended
for titrations with Hydranal-Composite. The titration
procedure is described in detail in section 5.1. Variations
to the procedure as a result of differences arising from
the sample matrix are discussed in section 8. Specific
procedures for many products are described in sections
9 to 13. Suitable instrumentation for these titrations is listed
in section 6.
2.1.3 The product line
There are currently four different Hydranal-Composites;
each one is designed for a specific application.
Hydranal-Composite 5 has a titer of 4.5 to 5.5 mg H O/mL .2
It is the preferred reagent for most applications. It contains
imidazoles, sulfur dioxide and iodine in diethylene glycol
monoethyl ether (DEGEE). Hydranal-Composite 5 is very
stable and has a shelf life of three years. The titer decay is
approximately 0.3 mg H O/mL per year.2
Hydranal-Composite 2 has a titer of 1.6 to 2.4 mg H O/2
mL and is used for the titration of samples with lower water
contents. It contains imidazoles, sulfur dioxide and iodine
in diethylene glycol monoethyl ether (DEGEE). Hydranal-
Composite 2 is ver y stable and has a shelf life of three years.
The titer decay is approximately 0.1 mg H O/mL per year.2
Hydranal-Composite 1 has a titer of 0.8 to 1.2 mg H 2
O/
mL and is used for the titration of samples with very low
water levels. It is distinguished from the other titrants by
its high reaction sensitivity, meaning that trace amounts of
water can be titrated rapidly. This reagent has a shelf life of
three years. The titer decay is approximately 0.1 mg
H2O/mL per year.
Hydranal-Composite 5 K is a special reagent intended for
the determination of water in aldehydes and ketones (hence
the designation “K”). Applications using this reagent are
described in sections 2.4 and 9.6. Hydranal-Composite 5 K
consists of the same components as Hydranal-Composite 5
Chapter 2. HYDRANAL reagents
HYDRANAL Manual Chapter 2: HYDRANAL reagents
HYDRANAL-
Composite
HYDRANAL-
Methanol dry,
HYDRANAL-
Methanol Rapid or
HYDRANAL-
CompoSolver E
1. Fill the burette with HYDRANAL-Composite
2. Add HYDRANAL-Methanol dry or HYDRANAL-
Methanol Rapid or HYDRANAL-CompoSolver E
into the titration vessel
3. Titrate it to dryness with HYDRANAL-Composite
4. Add the sample
5. Titrate the water content with HYDRANAL-Composite
Figure 2.1.2. General procedure for volumetric one-component titration.

4
and can therefore be used for any application. However, a
titration with this reagent is slightly slower because of its
modified composition.
Hydranal-Methanol Rapid contains accelerators for the KF
reaction and reduces titration times significantly.
Hydranal-Methanol dry is a medium for the titration vessel
and contains a maximum of 0.01% H O. For general2
applications the titration speed can be improved by the
addition of a titration accelerator, like Hydranal-Solvent
(section 2.2.3) or Hydranal-Buffer for Acids (section 2.7). An
efficient titration can be achieved in practice by using a 3:1
mix ture of methanol and Hydranal-Solvent as solvent for the
sample and working medium for the titration.
Hydranal-CompoSolver E contains accelerators and is
based on ethanol. It can be used instead of methanol.
Hydranal-Solver (Crude) Oil is the most useful working We recommend the following procedure for the two-
medium for titration in oils. It contains methanol, x ylene and
chloroform and fulfills the requirements of A STM D 4377- 0 0
method.
Hydranal-LipoSolver CM and Hydranal-LipoSolver MH are
special working media for titration in non-polar samples.
They contain a mixture of chloroform and methanol (CM) or
methanol and 1-hexanol (MH).
2.2 HYDRANAL-Solvent and HYDRANAL-
Titrant two-component reagents for
volumetric titrations
The two-component reagents consist of all the necessary
reactants for the titration, but in two different solutions.
Hydranal-Solvent is the solvent solution consisting of
sulfur dioxide and imidazole in methanol. Hydranal-Titrant
is a solution of iodine with a pre-determined titer (water
equivalent). Hydranal-Solvent E and Hydranal-Titrant E
contain ethanol instead of methanol as solvent.
In the two-component system, both Hydranal-Solvent and
Hydranal-Titrant are necessar y for the titration.
2.2.1 Applications
When combined Hydranal-Solvent and Hydranal-Titrant
are virtually a universal reagent for the determination of
water by KF titration. These reagents can be used with all
commercially available titration equipment. In practice, the
two-component reagent is preferred when rapid titrations
and highly accurate results are required. The t wo - component
system is more accurate due to its faster rate of reaction. By
reacting with the water faster it does not experience as much
influence from atmospheric moisture as the slower one-
component system. Both reagents are very stable: titrants
have a three year shelf life, while the solvents have a five year
shelf life. The titer of Hydranal-Titrant will not change as long
as the bottle remains tightly sealed.
component titration technique. Hydranal-Solvent serves as
the working medium; Hydranal-Titrant is used to titrate the
sample (see Figure 2.2.2).
This titration procedure is described in detail in section 5.2.
Variations in the procedure to accommodate different
sample matrices are given in section 8. Specific procedures
for many products are described in sections 9 to 13.
Note: Although the Hydranal-Solvent and Hydranal-Titrant
can be premixed and used as a one-component reagent, the
stability of the mixture is significantly reduced. We do not
recommend this practice.
Different grades of Hydranal-Solvent and Hydranal-Titrant
reagents are available for dif ferent applications.
Hydranal-Solvent is the preferred working medium for
the two-component titration techniques. It consists of a
solution of imidazole and sulfur dioxide in methanol and
has a nominal capacity of 7 mg H O/mL. The solution2
has been pre-dried to maximum water content of 0.02%.
Hydranal-Solvent has a five year shelf life, during which the
water content will not increase as long as the bottle remains
unopened.
HYDRANAL-
Titrant or
HYDRANAL-
Titrant E
HYDRANAL-
Solvent or
HYDRANAL-
Solvent E
1. Fill the burette with HYDRANAL-Titrant or
HYDRANAL-Titrant E
2. Add HYDRANAL-Solvent or
HYDRANAL-Solvent E to the titration vessel
3. Titrate it to dryness with HYDRANAL-Titrant
or HYDRANAL-Titrant E
4. Add the sample
5. Titrate the water content with
HYDRANAL-Titrant or HYDRANAL-Titrant E
Figure 2.2.2. General procedure for volumetric two-component titration.

5
Hydranal-Solvent E is the same as Hydranal-Solvent except
it contains ethanol instead of methanol. It is preferred from
safety (ethanol is less toxic than methanol) and solubility
(some samples are more soluble in ethanol) standpoints,
however should be used quickly af ter opening.
Hydranal-Solvent CM contains imidazole and sulfur dioxide
in a mixture of methanol and chloroform and was developed
for the determination of water in oils and fats. The capacity
for water of this solution is approximately 3 mg H O/mL .2
Hydranal-Solvent Oil contains imidazole and sulfur dioxide
in a mixture of methanol and a long-chain aliphatic alcohol.
It does not contain chloroform. Hydranal-Solvent Oil is
designed for the determination of water in oils and fats. The
capacit y for water of this solution is approximately 3 mg H O/2
mL. The Hydranal-Solvent CM and Hydranal-Solvent Oil
have dif ferent solubilizing proper ties, giving analysts choices
in the abilit y to dissolve oily samples.
For titration in oils also Hydranal-Solver (Crude) Oil can be
used in t wo-component system.
Hydranal-Titrant 5 is the standard titrating agent for general
applications. It is a methanolic solution of iodine with an
exact titer adjustment of 4.95 to 5.05 mg H O/mL. The titer2
remains unchanged even after prolonged storage, as long
as the bottle remains unopened. The titer however may drop
slightly through handling, since methanol is hygroscopic.
Hydranal-Titrant 5 E is the same as Hydranal-Titrant 5 except
the methanol has been replaced by ethanol.
Hydranal-Titrant 2 is a titrating agent for small amounts of
water. The titer is adjusted to 1.96 to 2.04 mg H O/mL . The2
methanolic solution of iodine can show a slight drop in titer
during handling.
Hydranal-Titrant 2 E is the same as Hydranal-Titrant 2 except
the methanol has been replaced by ethanol.
2.3 HYDRANAL -Coulomat reagents for
coulometric determinations
For standard coulometric KF titrations, two reagent
solutions, an anolyte (the solution about the anode) and a
catholyte (the solution about the cathode), are necessary.
The anolyte is a modified KF reagent containing iodide
instead of iodine. The Karl Fischer reaction occurs in the
anolyte [1]. The catholyte enables the counterpart cathode
reaction that must proceed so that the by-products of the
KF reaction produced at the cathode are not disturbed [1].
Coulometric cells without a diaphragm are also available. In
that case, the anodic and cathodic compartments are not
separated and only one reagent, the anolyte, is needed [14].
Hydranal products for coulometric KF titration are given the
name Hydranal-Coulomat.
2.3.1 Applications
Hydranal-Coulomat A and Hydranal-Coulomat CG are the
standard reagents for coulometric KF titration. Hydranal-
Coulomat AG, AD and AG-H are anoly tes free of halogenated
solvents, Hydranal-Coulomat CG is the corresponding
catholyte. Hydranal-Coulomat E is a new reagent where
most of methanol is replaced by ethanol. It is also free of
halogenated solvents.
The following general procedure is used for the coulometric
determination of water (see Figure 2.3.2).
This titration procedure is described in detail in section 5.3.
Alterations to the procedure due to the sample matrix are
given in section 8. Procedures for many specific samples are
described in sections 9 to 13.
Figure 2.3.2. General procedure for coulometric titration.
HYDRANAL-Coulomat CG
1. Fill the anodic compartment (A) with
Hydranal-Coulomat A/AG/AG-H/E
2. Fill the cathodic compartment (C) with
3. Switch on the instrument (cell is
automatically titrated to dryness)
4. Push the analysis button
5. Inject the sample
6. Record the water content at the end of
the analysis
7. Repeat steps 4-6
A C
HYDRANALCoulomat A,
HYDRANALCoulomat AG,
HYDRANALCoulomat AGH,
or HYDRANALCoulomat E

6
Hydranal-Coulomat A is the anodic reagent (anolyte) for
coulometric titration. It contains sulfur dioxide, imidazole
and iodide in a solvent mixture of methanol and chloroform.
It is preferred for cells with diaphragm. A volume of 100 mL
in the anodic compar tment will suf fice for the determination
of approximately 10 0 0 mg H O.2
Hydranal-Coulomat AD is a chloroform-free anolyte
reagent especially designed for coulometric cells without
a diaphragm.
Hydranal-Coulomat AG is a chloroform-free anolyte. It
contains two suitable bases, along with sulfur dioxide,
imidazole, iodide and methanol as solvent. It has a water
capacity of 1000 mg per 100 mL. Hydranal-Coulomat AG is
also suitable for use in coulometr y without a diaphragm.
Hydranal-Coulomat E contains the same components as
Hydranal-Coulomat AG, but the majority of the methanol
is replaced by ethanol. It is suitable for cells with and
without diaphragm.
Hydranal-Coulomat AG-H is an anoly te for the investigation
of hydrocarbons. It contains a long-chain alcohol and similar
components as Hydranal-Coulomat AG, but is preferred for
cells with diaphragm.
Hydranal-Coulomat AG-Oven is an anoly te with minimal and
ex tremely stable drif t. It was developed for the determination
of water in gases or with a K F O ven connected to a coulometer.
Hydranal-Coulomat Oil is an anolyte for the water
determination in oils, including crude oil. It contains
chloroform and xylene as the solubilizing agents. Hydranal-
Coulomat Oil is preferred for cells with diaphragm.
Hydranal-Coulomat CG is the catholyte free of halogenated
solvents. It contains a patented formulation containing
ammonium salts as the reactive component and methanol
as the solvent. A volume of 5 mL is sufficient for the
determination of 20 0-30 0 mg water.
Hydranal-Coulomat AK and Hydranal-Coulomat CG-K are
complementary, methanol-free reagents intended for the
coulometric determination of water in ketones and other
substances that react with methanol . Fur ther information on
these products can be found in sections 2.4 and 8.4.
2.4 HYDRANAL products for the
determination of water in aldehydes
and ketones
Historically, aldehydes and ketones have posed
problems for KF titration because they react with some
conventional reagents to produce acetals and ketals [1].
The water formed in this reaction is also titrated, leading
to erroneously high results and vanishing end points.
Additionally, a second side reaction, the well-known bisulfite
addition, can occur during the titration of aldehydes.
This unwanted side reaction consumes water leading to
erroneously low results [1].
We have developed and patented Hydranal reagents that do
not produce these side reactions, eliminating or significantly
reducing these sources of error. These innovations include
specific amines and alcohols not found in competitive KF
reagent formulations.
The reagent for the volumetric titration of water in aldehydes
and ketones consists of two components: Hydranal-
Composite 5 K and Hydranal-Working Medium K, Hydranal-
Medium K or Hydranal-KetoSolver.
Hydranal-Composite 5 K is the titrating reagent for the
determination of water in aldehydes and ketones. It consists
of a solution of imidazole, sulfur dioxide and iodine in
diethylene glycol monoethyl ether.
Hydranal-Working Medium K is the corresponding solvent
system for Hydranal-Composite 5 K titrant. It contains
2-chloroethanol and chloroform. Hydranal-Working Medium
K is added to the titration vessel and serves as the working
medium and as the solvent for the sample. Both solutions are
used like a one-component reagent, i.e. in accordance with
the procedures described in sections 2.1.2 and 5.1.
Hydranal-Medium K is a new, less toxic medium that can
replace Hydranal-Working Medium K .
Hydranal-KetoSolver is free of halogenated solvents. It gives
a slightly slower titration rate.
The Hydranal reagents described above can be used
for the determination of water in substances other
than aldehydes and ketones. The Hydranal-Medium K,
Hydranal-Working Medium K and Hydranal-KetoSolver
can act as the solvent for the determination of water in any
substance where methanol can interfere with the titration
and must be avoided. Further information can be found in
section 8.4.
Hydranal-Composite 5 K can be used as a universal titrating
reagent. It does, however, have a slower titration rate than
Hydranal-Composite 5 (refer to section 2.1.3). In many
cases, Hydranal-Medium K can be used in conjunction with
the standard volumetric reagent, Hydranal-Composite 5. For
the determination of water in aldehydes and cer tain reactive
ketones however, it is strongly recommended that only
Hydranal-Composite 5 K be used (section 9.6.1).
Hydranal-Coulomat AK is an anolyte for the coulometric
determination of water in ketones. It contains imidazole,
sulfur dioxide and iodide dissolved in a suitable solvent
mixture. Its capacity is approximately 100 mg of water
per 10 0 mL.
Hydranal-Coulomat CG-K is the corresponding catholyte.
It does not contain halogenated hydrocarbons. The water
capacit y of 5 mL Hydranal-Coulomat CG-K is 10 0 mg.

7
Both Hydranal-Coulomat AK and Hydranal-Coulomat CG-K
reagent solutions are used in the same way as the standard
Hydranal reagents for coulometry, i.e. according to the
procedures described in sections 2.3.2 and 5.3.
2.5 HYDRANAL water standards
It is good analy tical practice to check the titer of KF titration
reagents prior to performing new titrations, especially if the
reagent bottle has been previously opened. The titer can be
calibrated using a number of substances that have differing
advantages and varying limitations [1]. We therefore
recommend Hydranal-Water Standards with an exactly
confirmed water content for:
• Titer determination
• Monitoring precision and accuracy
• Validation and inspection of Karl Fischer titrators
according to ISO, GMP, GLP and FDA guidelines
All of Hydranal-Water Standards are verified against NIST
SRM 289 0 and some additionally against NMIJ CRM4222-a.
They are supplied with detailed instruction for use and ten 8 mL glass ampoules.
depending on their quality either with Report of Analysis
(RoA) or Certificate of Analysis (CoA) showing the exact
water content.
Liquid standards consist of a solvent mixture with specific
composition and precisely determined water content.
They are packaged under argon in pre-notched single-use
glass ampoules.
Solid standards contain defined amounts of chemically
bound water suitable for both general use as well as for the
Karl Fischer oven. These standards are packed in amber
glass bottles.
In 2014, Hydranal Technical Service in Seelze completed its
combined accreditation according to ISO/IEC 17025 and
ISO Guide 34, the so-called “Gold Standard Accreditation”,
which is the highest achievable quality level for producers
of Certified Reference Materials (CRMs). With the
double accreditation, Hydranal introduced the very first
commercially available CRM Water Standards for Karl
Fischer titration.
Hydranal-Standard Sodium Tartrate Dihydrate
Water content: ~15.66%
Sodium tartrate dihydrate is mentioned in some
regulations as the primary standard for KF applications.
Sodium tartrate forms a dihydrate, which, under normal
conditions, remains stable and does not loose or adsorb
moisture. This dihydrate has a water content of 15.66%
plus quite small amounts of adhered water, which are
qualified by volumetric KF titration. The product is
presented in a finely-powdered form that dissolves
relatively quickly but still limited in methanolic KF solvents.
Hydranal-CRM Sodium Tartrate Dihydrate
Certified Reference Material for general KF applications.
This product provides similar performance as the “normal”
standard quality above but with higher grade on quality
control and documentation.
Hydranal-Water Standard 10.0
Water content: 10.0 mg/g = 1.0%
This standard is intended for calibrating volumetric KF
reagents. The liquid nature makes it suitable for application
in all known KF media without any limitations regarding
solubility. One package contains ten 8 mL glass ampoules.
Depending on application the content of one ampoule can
enable a triple-determination.
Hydranal-CRM Water Standard 10.0
Certified Reference Material for calibrating volumetric KF
reagents. This product provides similar performance as the
“normal” standard quality above but with higher grade on
quality control and documentation. One package contains
This standard is intended to verify coulometric water
determinations or the volumetric determination for low water
levels. One package contains ten 4 mL glass ampoules.
Depending on application the content of one ampoule can
enable a triple-determination.
Hydranal-CRM Water Standard 1.0
Certified Reference Material intended to verify coulometric
water determinations. This product provides similar
per formance as the “normal ” standard qualit y above but with
higher grade on quality control and documentation. One
package contains ten 4 mL glass ampoules.
T his st andard is intended to verif y coulometric determinations
of small amounts of water. One package contains ten 4 mL
glass ampoules. Depending on application the content of
one ampoule can enable a triple-determination.
Hydranal-Water Standard 0.1 PC
This standard is intended to verify coulometric
determinations of small amounts of water. It has improved
stabilit y compared to Hydranal-Water Standard 0.1: shelf life
increased from t wo years to three years and can be stored at
room temperature instead of 2-8°C. One package contains
ten 4 mL glass ampoules. Depending on application the
content of one ampoule can enable a triple-determination.

8
Hydranal-Water Standard Oil
Water content: approx. 10 ppm (0.001%)
Mineral-oil based matrix standard for KF titration in oils.
Depending on the individual Lot in most cases this standard
contains less than 10 ppm water and is intended to check
the KF determination at the absolute low trace level. One
package contains ten 8 mL glass ampoules.
These t wo solid standards are intended to check the reliabilit y
of a Karl Fischer ovens:
Hydranal-Water Standard KF Oven 14 0 -160°C
Water content: ~5%, based on lactose
Hydranal-Water Standard KF Oven 220 -230°C
Water content: ~5.55%, based on potassium citrate
2.6 HYDRANAL for back titration
The back titration method, described in section 5.4, is rarely
used. However, we supply a reagent for volumetric back
titration applications:
Hydranal-Water-in-Methanol 5.0
This solution contains 5.0 0 ± 0.02 mg H O/mL .
2
2 .7 HYDRANAL buffers
The KF reaction is pH dependent, with pH 5-7.5 being the
ideal range. Strongly acidic samples slow the reaction and
must be neutralized without inducing an alkaline reaction of
the working medium prior to star ting the titration. Details are
given in section 8.6.
Hydranal-Buffer for Acids is a suitable buffer solution to
stabilize the pH to within the ideal range of 5-7. It contains
imidazole and has a buffer capacity of 5 mmol acid per
mL. Hydranal-Buffer for Acids also enhances the visual
indication of the end point as the yellow background color is
suppressed. A distinct color change to brown can be better
observed.
Hydranal-Buf fer for Bases is a ready-made working medium
for water determination in bases. It contains salicylic acid
and has a buf fer capacit y of 1 mmol base per mL.
Solid buffer substances, Hydranal-Benzoic Acid, Hydranal-
Salicylic Acid and Hydranal-Imidazole, can be used together
with standard KF reagents.
2.8 HYDRANAL auxiliary products
Karl Fischer titration is applied to multifarious substances.
The nuances in sample proper ties influence the Karl Fischer
titration differently. There are a number of ways to adjust
the working conditions in order to enable a direct titration
of the sample and avoid complicated and error-prone pre-
dissolution and pre-extraction steps. In some cases the
addition of solubilizers is recommended.
Hydranal-Formamide dry
Solubilizer, max. 0.02% water.
Hydranal-Chloroform
Hydranal-Xylene
Both titration vessel and reagent bottle should be protected
from infiltration from atmospheric moisture by using drying
tubes filled with proper dr ying agent:
Hydranal-Humidity Absorber
Dr ying agent for air and gases. Amorphous alumina silica gel
with indicator. Water absorption capacit y <25%.
Hydranal-Molecular Sieve 0.3 nm
Dr ying agent for air and gases without indicator.
Water absorption capacit y >15%.
These t wo reagents can be used for rough testing of
volumetric titration performance:
Hydranal-Sodium tartrate dihydrate
Test solution for volumetric titration.
Hydranal-Standard 5.0
Test substance for volumetric titration.
Water content: ~5.0 0 mg/mL.
For rough measurements without a titrator, special test kits
for visual water determination according to Karl Fischer can
be used:
Hydranal-Moisture Test Kit
The set contains syringes, titration vessel and reagents:
2 x 500 mL Hydranal-Solvent E, 100 mL Hydranal-Titrant 5
E and 10 0 mL Hydranal-Standard 5.0.

9
The Hydranal reagents, initially only intended as an
alternative to the original pyridine - containing reagents, have
surpassed the popularity of classical Karl Fischer solutions
in many application areas. Many of the Hydranal advances,
like more effective bases and safer reagents have equaled
the replacement of pyridine in importance; an unexpected
but certainly welcome observation. The classical KF
reagents titrate very slowly and with vanishing end points
making it dif ficult to determine the actual end of the titration.
Accurate reagent consumption, and hence the accurate
water measurement, depends on the working conditions
and the results of the analysis are somewhat uncertain
when using the classical KF reagents. A significant problem
with slow titration is that moisture has time to permeate into
the system. The uncertainty of the results increases as the
expected amount of water in the sample decreases. Also, the
determination of trace amounts of water using the original
KF reagents is nearly impossible because of the insuf ficient
basicit y of the pyridine used in those reagents [1].
3.1 Titration speed
Hydranal reagents are characterized by a rapid course of
titration. Figure 3.1 compares the course of 3 titrations of
4 0 mg of water.
The titration using a pyridine-containing one-component
reagent takes approximately ten minutes (curve C).
Hydranal-Composite 5 shortens this titration time to
about four minutes (curve B). The most rapid titration,
taking less than two minutes, is achieved with the Hydranal
two-component reagent (curve A). The high reactivity of
Hydranal reagents has been achieved by an optimization
of the reactants and an adjustment of the pH of the total
titration system.
3.2 End point stability
The titration curves in Figure 3.1 show that the end point
stability improves as the titration time is reduced. The
advantages of Hydranal reagents become even more
apparent when trace amounts of water are determined, as
depicted in Figure 3.2. A definite end point was reached
using the Hydranal two-component reagent (curve A)
while the titration curve of the pyridine-containing KF
reagent (curve C) gives the impression that the instrument
aborted without having reached a finite end point. This is of
particular significance when determining small amounts
of water; exactly the case when the solvent is titrated to
dryness by the instrument. Each uncertainty in the pre-
titration phase of the analysis adds to the inaccuracy of the
resultant determination of water content.
2
H O [mg]2
t [min]
40
30
20
10
0
4 6 8
A B C
A C
2
H O [mg]2
t [min]
2
1
0
4 6 8
HYDRANAL Manual Chapter 3: The advantages of HYDRANAL
Chapter 3. The advantages of HYDRANAL
Figure 3.1. Titration of 40 mg of water using:
A - Hydranal two-component reagent;
B - Hydranal one-component reagent;
C - pyridine-containing one-component reagent.
Figure 3. 2. Titration of trace amounts of water using:
A - Hydranal two-component reagent;
C - pyridine-containing reagent.

10
3.3 Accuracy
The greater reliability of Hydranal reagents was tested by
running a series of side-by-side water determinations on
Hydranal reagents and a pyridine-containing KF reagent. In
each case, the titer of each titrant was standardized using
100 mg of water. Different amounts of water were titrated
by each reagent and the standard deviation (scatter) of
t went y analyses was calculated. The results are presented in
Table 3.3.
The consumption of the Hydranal two-component reagent
was directly proportional to the total water content over the
entire range tested, clearly indicating that the KF reaction
remains stoichiometric. The pyridine-containing KF reagent
showed a systematic deviation of +2.5% in the range
10-20 mg H O and a scatter of 1-2%, which infers a2
total error of as much as 4%. Hydranal-Composite one-
component reagent showed a systematic error of 0.5%,
which is still bet ter than the pyridine-containing KF reagent.
The most accurate results were obtained using the Hydranal
two-component reagent.
In order to assure a stoichiometric course of the KF
reaction, certain fundamental requirements must be met
and several potential interferences must be avoided. The
working medium, which is the solvent used to dissolve and
titrate the sample, and the pH of the system are the two
most important considerations.
HYDRANAL Manual Chapter 3: The advantages of HYDRANAL
Table 3.3. Error and scatter in the determination of water [1]. 20 individual analyses
Water content KF reagent
containing pyridine
One-component
HYDRANAL-Composite
Two-component
HYDRANAL-Solvent &
HYDRANAL-Titrant
100 mg ± 0.44% ± 0.30% ± 0.20%
50 mg +0.56 ± 0.62% +0.06 ± 0.24% +0.01 ± 0.30%
20 mg +1.68 ± 0.93% +0.33 ± 0.60% +0.02 ± 0.25%
10 mg +2.59 ± 1.85% +0.84 ± 0.6% -0.1 ± 0.5%
5 mg +2.40 ± 2.5% +0.72 ± 1.2% +0.2 ± 1.0%

11HYDRANAL Manual Chapter 4: Chemical fundamentals behind Karl Fischer titration
4.1 Working medium
The working medium is the solvent or solvent mixture in
which the sample is dissolved and in which the KF titration
is carried out. The correct working medium assures the
stoichiometry of the KF reaction. The working medium
must be able to dissolve the sample and the products
of the titration reaction and allow confident end point
determination [1]. Only a few solvents can fulfill all of
these requirements.
Methanol is the preferred choice for a working medium,
it permits a rapid and stoichiometric course of the KF
reaction. Most samples dissolve easily in methanol, and
it gives a sensitive and reliable indication of the end point.
Often, other solvents are added to the methanol, although
the methanol content should always be at least 25%.
1-Propanol, ethanol and other long-chained alcohols are
better at dissolving lipophilic molecules than methanol
and can be added to the methanol to improve solubility of
the sample (section 8.1). Occasionally, they can be used
alone as the solvent while developing methods for these
t ypes of compounds (section 8.4).
2-Methoxyethanol (ethylene glycol monomethyl ether)
and 1-methoxy-2-propanol are other alcohol solvents.
They are preferred when side reactions (esterification, ketal
formation, etc.) can occur in the presence of methanol.
Titrations in these solvents are slower than in methanol
(section 8.4).
We have investigated 2-chloroethanol as a methanol application, a pH range of 4-7 is acceptable.
alternative or additive. It suppresses side reactions and
enables a rapid KF reaction (section 8.4).
Chloroform is a good solvent for solubilizing fats and can
be combined with methanol. The methanol content should
be at least 25% and preferably 50% (see section 8.2). The
use of 100% chloroform changes the stoichiometr y of the
KF reaction and is therefore not suitable to use on it own.
Formamide improves the solubility of polar substances
and can be mixed with methanol for the determination
of water in proteins (section 8.3). The methanol content
should not be less than 50% [1]. A 30% proportion of
formamide usually suf fices and is preferred.
Other solvents can be used in specific cases. Caution is
called for when using aprotic solvents as they alter the
stoichiometry of the KF reaction towards the Bunsen optimal range. When this is suspected, the pH should be
equation [1], i.e. the titer of the titrant appears erroneously
high. The change in titer does not remain constant, but
depends on the ratio of the alcohol to the aprotic solvent.
This ratio changes throughout the titration since the titration cell because the pH electrode will introduce water
titrating agent contains alcohol. The result is an indefinable
ratio, a continuously changing stoichiometry and portion of the working medium that has been taken from
inaccurate results. To be accurate, this approach requires
an exact determination of the titer under the identical
working parameters. Therefore, we do not recommend the
use of pure aprotic solvents as the working medium for
KF titrations.
These fundamental rules also apply for KF titrations with
Hydranal reagents. With the one-component reagent
Hydranal-Composite, the working medium can be
selected by the user. Methanol is used in the majority of
cases because of the advantages previously mentioned.
Mixtures of methanol and chloroform or methanol and
formamide are used in specific cases in order to improve the
solubility of the sample. Hydranal-CompoSolver E, which is
based on ethanol, can also be used. When working with the
two-component reagent, Hydranal-Solvent, which contains
methanol as the solvent, is used as the working medium. The
addition of chloroform or formamide is possible in specific
cases. Replacing these solvent components by other
solvents is not permissible. Proven mixtures of solvents are
described in detail in section 8.
4.2 pH
In the ideal pH range 5-7.5, the Karl Fischer reaction runs
quickly and stoichiometrically. At higher pH values a side
reaction occurs that consumes iodine. It can be observed
by a reversal of the end point. In stronger acidic conditions
the reaction constant of the KF reaction decreases. Thus
at pH 2-3 the reaction appears much slower and at pH 1
the KF reaction does not take place at all [1]. Depending on
T he titration of water produces acids that must be neutralized.
The Hydranal reagents contain imidazole as the base to
neutralize these acids and buffer the titration system. The
pH is thus stabilized around the ideal value of 5, ensuring a
rapid and stoichiometric course of the reaction.
The pH balance of the titration can be upset by the
introduction of large amounts of strong acids or bases, for
example, when the water content of such substances is to
be determined [1]. These substances must be neutralized
by adding an appropriate weak base or acid or a buffer
solution to the working medium. Details are given in
section 8.5 and 8.6.
Sluggish or vanishing end points can be an indication
of a fluctuation of the pH of the system outside the
measured. A glass pH electrode, previously calibrated in
an aqueous solution, can be used for this. The pH of the
system should not however be determined directly in the
to the system. Instead, the pH should be measured on a
the titration cell with a few drops of water.
Chapter 4. Chemical fundamentals behind Karl Fischer titration

12
The log K vs. pH curve for a KF titration appears in
Figure 4.2. Note the optimal range of pH 5-7.5 over which
the log K does not change significantly.
HYDRANAL Manual Chapter 4: Chemical fundamentals behind Karl Fischer titration
Figure 4. 2. Dependence of the reaction rate constant
K on the pH ( Verhoef, J. C. and Barendrecht, E.;
Mechanism and Reaction Rate of the Karl-Fischer
Titration Reaction. J. Electroanal. Chem. 1976, 71,
305-315).
log K
pH
4
2
0
2 4 6 8 10

13
The KF titration has been carried out in many different
ways in the past 70 years. Originally, organic solvents
were titrated directly with the KF reagent. Later, solvents
used as diluents were introduced where water content was
determined by so-called “blank titrations” and subtracted
in the subsequent calculations. Today, a suitable solvent is
usually added to the titration vessel, dehydrated by a pre-
titration and used as the working medium for the titration
of the sample. The function of the working medium was
covered in more detail in section 4.1.
Three basic forms of the KF titration have evolved:
• Volumetric titration using a one-component reagent
• Volumetric titration using a two-component reagent
• Coulometric titration
Volumetric titrations are used when water content is high,
i.e. 1-100 mg per sample.
Coulometry is a micro-method and is particularly suitable
for samples with low water content, on the order of 10 µg
up to 10 mg of water per sample.
The fundamental techniques of each of the three titration
methods are described in this section. They can be used
to analyze many different substances. When difficulties
in analyzing a sample are encountered, modifications to
the basic technique are made. Suggested variations to the
titration procedures to accommodate different sample titration also induces an error of the same magnitude in
matrices are given in section 8. Titrations of specific the subsequent determination of water. A perfectly dried
products are described in sections 9-13.
5.1 Volumetric titrations using the one-
component reagent HYDRANAL-Composite
Hydranal-Composite are the one-component KF reagents.
They are preferred reagents for KF titration because of
convenience – they contain all the necessary reactive
components in one solution. The working medium it
requires (the solvent for the sample) is not prescribed and
can be chosen by the analysis within limits. Hydranal-
Composite can be used with all commercially available
titration equipment with only minor changes to the working
procedures. The sequential steps of a titration of water
using the one-component reagent are described in the
following section.
5.1.1 Addition of the reagent
First, the burette is filled with Hydranal-Composite. With
many instruments, the original bottle is connected to
the equipment. Whatever the set-up, it is imperative that
the burette, stock vessel and their interconnections are
absolutely dry. Residual water can cause local changes in
the titer and lead to errors in the results. The stock vessels
should be protected from infiltration of atmospheric
moisture by using dr ying tubes (see section 6.4).
5.1.2 Addition of the working medium
Next, 20-40 mL of working medium are added to the
titration vessel. The amount of working medium added
depends on the size of titration cell and on the size of the
sample to be titrated (see section 6.5). The titration cell is
closed immediately after the addition of working medium
in order to keep the amount of unavoidable atmospheric
moisture to an absolute minimum. Hydranal-Methanol dr y
or Hydranal-Methanol Rapid or Hydranal-CompoSolver E
can be used as a working medium.
5.1.3 Pre-titration
Next, the solvent in the titration vessel is titrated to
dryness with Hydranal-Composite. This pre-titration is
important because it removes the residual water that was
in the solvent and the moisture adhering to the surfaces in
the cell and on the electrode. The atmosphere of the cell
is also dried of moisture. A completely anhydrous working
medium is achieved in this way. The pre-titration must
be carried out very carefully since any error will influence
the subsequent determination of the water content of
the sample. Also proper stirring speed should be applied.
A titration to a stable end point is the prerequisite for a
reliable analysis. Because the amount of water removed by
the pre-titration is relatively small, this titration is carried
out as slowly as possible. An excess of reagent during pre-
titration cell has a maximum drif t consumption of 0.01 mL
of KF reagent per minute.
5.1.4 Weighing the sample
After pre-titration of the working medium and titration
cell to dryness, a pre-determined quantity of the sample
to be investigated is added to the working medium. The
cell is opened for as short a time as necessary and then
closed again immediately after the sample was added to
keep intrusion of atmospheric moisture to an absolute
minimum. Recommended sample addition techniques
(syringes, pipettes, weighing boats, etc.), are described in
detail in section 7.3.
The size (mass or volume) of the sample per titration
depends on its water content, the volume of the burette,
the titer of the titration agent and the desired accuracy.
Details are given in section 7.2. We recommend using as
much sample as to consume approximately half a burette
volume of reagent. When using Hydranal-Composite 5
(water equivalent 5 mg H O/mL) and a 10 mL burette, the2
amount of sample is chosen so it contains approximately
25 mg of water. In many cases, like in the determination
of trace amounts of water, the sample size will be
significantly lower.
Chapter 5. Standard procedures for KF titrations
HYDRANAL Manual Chapter 5: Standard procedures for KF titrations

14
5.1.5 Titration of the water content
Once the sample has been added, the titration should be
started immediately. The dosage rate of the titration agent
can be adjusted to the anticipated amount of water. The
titration rate should be rapid initially, but reduced when
the end point is imminent. Modern KF instrumentation
automatically adjusts the titration rate to the amount of
water still remaining in the titration vessel.
A definite determination of the end point is as important
as the pre-titration step. Generally, one titrates to an end
point of 10 seconds stability (section 5.6). A stable end
point is a significant indication of the course of a titration
with no complications. A vanishing end point indicates that titrations. Modern instruments allow an automatic
the water in the sample was released too slowly or that
there were interferences from side reactions.
5.1.6 Calculation of the results
After a stable end point has been reached, the amount of
Hydranal reagent used is read from the burette scale. The
water content is calculated from the volume consumed
and the water equivalent (titer) of the reagent:
a  WE
a WE
10  e
where:
a = the consumption of reagent in mL
WE = water equivalent (titer) of the reagent in
mg H2O/mL
e = weight of the sample in g
The following formula is applied for the statistical
evaluation of a series of titrations:
where:
x i
= result of each analysis
n = number of analyses
m = mean
S = standard deviation
5.1.7 Replacement of the working medium
Following the completion of a titration, the spent solutions
should be removed from the titration cell. Most instruments
are equipped with pumps that not only empty the titration
cell but also dry the atmosphere within it. A plastic wash
bot tle proves ver y useful for the manual removal of the spent
solution (section 6.5). The titration cell should be opened for
as short time as possible in order to keep the introduction of
atmospheric moisture to an absolute minimum.
Usually the titration cell is immediately refilled with fresh
solvent and dehydrated by a pre-titration. Automatic
titration instruments are programmed for continuous
“conditioning”. The solvent is continuously kept at its
equivalency point. Thus, a prepared working medium and
a dr y titration cell are constantly available and ready for the
next sample.
Sequential titrations in the same working medium are
possible. The solvent mixture of the previous titration is
immediately used as the working medium for the titration
of the next sample. In this way, the use of a fresh solvent
and a pre-titration for each titration is not required. When
performing sequential titrations, the substance being
investigated should be of the same t ype. Also, the methanol
content in the working medium must not fall below 25% or
the end point may be altered.
5.2 Volumetric titrations using the two-
component reagent HYDRANAL-Titrant (E)
and HYDRANAL-Solvent (E)
The Hydranal two-component system consisting of
Hydranal-Titrant and Hydranal-Solvent is distinguished by
a rapid titration rate, stable end points and highly accurate
results. The titer of Hydranal-Titrant is absolutely stable as
long as moisture does not penetrate into the reagent.
A proven method has been established when using
two-component reagents. Hydranal-Solvent serves as
the working medium and is added to the titration cell.
Hydranal-Titrant is used as the titrating agent and is added
to the cell from the burette. This reagent can be used
with all commercially available equipment. The actual KF
titration is carried out in a similar fashion as with the one-
component reagents described above.
5.2.1 Addition of HYDRANAL-Titrant/Titrant E
First, Hydranal-Titrant is added to the burette, i.e. it is
the stock vessel for the burette. Stock vessel, valves and
interconnections must be completely dry. The stock
vessels are protected from atmospheric moisture by the
addition of dr ying tubes (see section 6.4).
)
Mean
Standard deviation
Sabs =
Srel =
1
n
100 · Sabs
m
m =
xi
2
- 1
n ( xi
2
n - 1
%
xi
mg H O =2
% H O =2

15
5.2.2 Addition of HYDRANAL-Solvent /
Solvent E
Next, 20-40 mL of Hydranal-Solvent are added to the
titration vessel . The exact amount added depends primarily
on the size of the titration cell. The titration cell is sealed
immediately following the addition of Hydranal-Solvent 5.3 Coulometric titrations with HYDRANAL-
in order to keep the unavoidable intrusion of atmospheric
moisture to a minimum.
5.2.3 Pre-titration
The Hydranal-Solvent added to the titration vessel is
then titrated to dryness with Hydranal-Titrant. This pre-
titration is analogous to that of the one-component
reagent and requires the same care (see section 5.1.3).
The instrumentation used should be equipped with a
particularly fast stirrer to ensure complete mixing of
reactants within the cell. The stir rate should, however,
preclude the inclusion of potential moisture from the
cell atmosphere.
5.2.4 The sample
The same rules apply as for the one-component reagent
(section 5.1.4). In addition, it must be remembered that
the Hydranal-Solvent has a defined and limited capacity
for water that cannot be exceeded (see section 2.2.3).
Usually, an effective water capacity of approximately 7 mg
H O per mL of Hydranal-Solvent is anticipated, i.e. if 20 mL2
Hydranal-Solvent are available, a maximum water content
of 140 mg H O can be titrated.2
5.2.5 Titration of the water content
The titration of water is started immediately after the
sample has been added to the vessel. The initial stages of
the titration should be rapid, but reduced in rate as the end
point approaches. A stable end point must be achieved or
the results will be in doubt (see section 5.1.6).
The results are calculated in the same manner as for the
one-component reagent (see section 5.1.6).
5.2.7 Replacement of HYDRANAL- Solvent /
Solvent E
As with a one-component reagent, following completion of
the titration the spent working medium should be removed
from the cell. Fresh Hydranal-Solvent is then added and
the pre-titration repeated, ensuring a prepared working
medium ready for the next titration.
Subsequent titrations are also possible using the two-
component titration system. However, the water capacity
(7 mg H O/mL) of the solvent component must be taken2
into consideration. If 20 mL of Hydranal-Solvent have been
applied, a maximum of 28 mL of Hydranal-Titrant 5 or
70 mL of Hydranal-Titrant 2 can be consumed during the
subsequent titrations. Otherwise, the water content of the
solvent component will be exceeded and accurate results
will not be obtained.
Coulomat A /AG/E/AG-H/AG-Oven and
In coulometric titration of water, the iodine required for the
KF reaction is produced by anodic oxidation of iodide [1]:
2 I⁻ - 2 e⁻  I2
The iodine reacts with the water present according to the
Karl Fischer reaction (see section 1.3). Iodine is consumed
as long as water is present. An excess of iodine indicates
the end point of the titration. Because the amount of water
titrated is proportional to the total current consumption
(current X time), the water content can be determined from
the current required for the titration.
Because the titration current is low, a maximum of 5-10 mg
H2
O can be determined in an economically acceptable time
period of 10 minutes. Coulometry is principally intended
for the determination of water in substances with low
water content (0.1-0.0001%). Particular advantages are
to be seen in the ppm range. This is a micro-method and
is therefore the ideal complement to volumetric titration
methods for smaller amounts of water.
In practice, commercially available instruments directly
indicate the water content, either in µ g H2
O or ppm H2
O.
The coulometric cell is the main component of the
equipment. The most commonly used cell consists of an
anodic compar tment, where the Karl Fischer titration takes
place, and a smaller cathodic compartment where the
corresponding cathodic reaction (a reduction of protons,
hydrogen ions) occurs. The anodic compartment contains
the necessar y anoly te, whereas the cathodic compar tment
contains the suitable catholyte. The compartments are
separated by a diaphragm that prevents an interchange of
the two reagent solutions.
The purpose of each solution is different. The elemental
iodine generated in the anodic compartment of the cell
reacts with the other reactants ultimately consuming the
water in the sample. The anolyte is basically a modified KF
solution. It enables the anodic oxidation of iodide to iodine
with a 100% yield of current. The counterpart reaction,
which the catholyte must be capable of producing, takes
place in the cathodic compartment. Since diffusion of
the reactive components cannot be ruled out in spite of
the diaphragm separating the two compartments, the
components of the catholyte must be compatible with
the anolyte. Therefore, we cannot recommend the use
of an anolyte in the cathodic compartment. This would
enhance the danger of reductive products from the
cathode diffusing through the diaphragm to the anode.

16
A subsequent oxidation by elemental iodine leads to
erroneously higher water content results.
Hydranal-Coulomat A/AG-H and Hydranal-Coulomat
CG are reagents that have been developed especially for The amount of reagent used depends upon the
coulometric cells with a diaphragm. Hydranal-Coulomat
A/AG-H is the anolyte, Hydranal-Coulomat CG is the
catholy te (see section 2.3.3). Their proper use is described
in the following sections. When handling the reagents,
particular care should be taken to ensure the exclusion of
moisture since coulometry is a micro-method and even
the smallest amounts of water can result in serious errors.
A 1 mL volume of normal laboratory atmosphere contains
about 10 µg of H O, a value easily detected by the sensitive
coulometric method. The absolutely anhydrous titration
2
cell must therefore never be exposed to the atmosphere,
not even when adding the sample. Thus the sample should
be injected into the cell by a syringe through a septum.
Coulometric cells without a diaphragm consist of only one
chamber. The anode and cathode reactions take place in
the same electrolyte solution - the anolyte. The cathode
reaction must not produce any by-products that could be
oxidized and give the impression of extra water in the cell.
Hydranal-Coulomat AD has been developed especially
for coulometric cells without a diaphragm. Hydranal-
Coulomat AG/E /AG-Oven are also suitable for this form of
coulometric titration.
Coulometric titration is in principle very easy to carry out.
The machine is switched on and the sample is injected
into the sealed cell via a syringe through a septum. After
a few minutes, the water content of the sample is digitally
displayed by the machine. The next sample can be
injected immediately.
5.3.1 Filling the anodic compartment with
HYDRANAL-Coulomat A/AG/E/AG-H/
AG-Oven
It is important that the titration cell be completely dry.
Once the spent reagent from the previous determination
has been removed, the cell has to be refilled with fresh
reagent solution. If the cell was dismantled for cleaning
or other reasons, it must be dried at 50°C in a drying
cabinet prior to using it again. The dr ying of the diaphragm
requires special care. Consult the titration instrument
manufacturer’s instructions.
A slight excess of iodine during the manufacture of
Hydranal-Coulomat A /AG/E /AG-H/AG-Oven removes the
last traces of moisture from the reagent. The light brown
color of the reagent can disappear during transport and/
or storage because the solution is hygroscopic. When
colorless, any absorbed moisture can be removed by adding
several drops of Hydranal-Titrant, or any other 5% solution
of iodine in methanol, until the slightly brown coloration of
the reagent has been re-established. An excess of iodine
should, however, be avoided. The solution is added to the
anodic compar tment of the coulometric titration cell using
a dry funnel. During this process the coloration should
disappear again.
titration instrument. Usually, it requires approximately
100-150 mL. The titration cell is immediately closed after
the addition of reagent. A titration cannot be initiated if
the solution still shows an excess of elemental iodine, in
which case an appropriate addition of water, or preferably
aqueous methanol, will remove the iodine and ensure a
properly functioning anolyte.
5.3.2 Filling the cathodic compartment with
The cathodic compartment is filled with Hydranal-
Coulomat CG . The amount of reagent used is in accordance
with the manufacturer’s instructions, usually 5 mL . Relative
to the anolyte, the level of the catholyte in the cathodic
compartment should be slightly lower in order to prevent
diffusion into the anodic compar tment.
The cathodic compartment must also be anhydrous,
as otherwise the moisture will diffuse into the anodic
compar tment and cause sluggish end points and erroneous
results. This solution is dehydrated in a similar manner. A
slight excess of elemental iodine is not detrimental.
5.3.3 Drying the titration cell
The design and construction of the titrator is such that the
titration cell is self-dr ying upon initiation of the instrument .
A titration cannot be star ted unless the titration cell is dr y.
The instrument determines and indicates the degree of
dryness of the equipment automatically. This is shown as
a “drift” or “background” in µg H O/min or µg H O/sec ,
depending on the instrument. It reflects the amount of
2 2
water that the equipment removes per minute, i.e. residual
moisture or penetrating moisture. Other instruments
indicate only the background titration current.
The drift of the instrumentation used for the coulometric
determination of water should not exceed 50 µg H O/min.
The drift value of a freshly replenished titration cell should
not exceed 10 µg H O/min. Ideally 4 µg H O/min can
be achieved.
2
2 2
The drift can increase during a series of determinations.
This does not appreciably influence the accuracy of
the analyses as the instrumentation automatically
compensates for the inherent drift value. This is only true
when the drif t rate is relatively stable.
This self-dehydration process exists only for the anolyte.
Moisture retained in droplets in the cell and moisture
adhering to the walls is slowly released and is the cause
of high drift values. This residual moisture can be quickly
removed by gently shaking the filled titration vessel.

17
Moisture from the cathodic compar tment can sometimes
be the cause of a high drift resulting from the slow
diffusion of water through the diaphragm into the anodic
compartment. Reductive substances produced in an
unsuitable (or spent) catholyte have the same effect.
Therefore we highly recommend replacing the catholyte
at least once a week, irrespective of how long the anolyte
was used.
5.3.4 Addition of the sample
The drift should be controlled before the sample is added.
In order to obtain reliable drift compensation by the
instrument, the drift should be stable. Some instruments
will go into “wait” mode and not titrate when the drif t is too
high or not suf ficiently stable.
The titration is initiated by pressing the start button. The
liquid sample to be analyzed is then injected through the
septum into the anolyte. The addition of solid samples
should be avoided, as the titration cell should not be
opened. Solid samples can be dissolved in suitable solvents
and added in solution form.
Also, the moisture can be evaporated from the solid sample
in an oven, collected and added as a vapor to the titration
cell (see section 8.11). Gaseous samples are introduced
into the anolyte via a gas inlet tube. Further details are
given in section 8.10.
The sample should always be weighed by difference. filled with Hydranal-Coulomat A/AG/E/AG-H/AG-Oven,
The size of the sample depends on the anticipated water
content and the desired accuracy. The optimum sample
size can be easily calculated (see section 7.2). For practical
reasons, the sample size should not exceed 10 mL. The
volume of a coulometric titration cell will hold another
50 mL, approximately. A single titration of 10 mL of sample
means a total of 5 determinations possible per reagent fill.
The smallest sample size is dependent upon the desired
accuracy. The reproducibilit y of results varies from 1-10 µg
H O per determination depending on the instrument used.
2
Generally, 0.5-5.0 mL samples in liquid form are added.
Gaseous samples range from 100 mL to 10 L.
Modern coulometric titration equipment indicates the
amount of water digitally in mg and thus enables an easy
conversion to mass units. Most instruments will show the
results in mass or volume units, i.e. % or ppm if the sample
size was entered.
5.3.6 Reliability
Coulometry is often referred to as an “absolute method,”
which implies the “absolute” and total reliability of the
results. Only the total current measured is absolute. The capacity limit of Hydranal-Coulomat A/AG/E/AG-H/
Whether the current measured is proportional to the AG-Oven is seldom reached. The chemical composition
actual amount of water in the sample cannot be assured
absolutely. There are many causes for the errors in titration
results. Inaccurate addition of the sample, moisture in the
titration cell, spent or unsuitable reagents, penetration
of reductive substances from the cathodic compartment
through the diaphragm, side reactions that produce water,
poisoned electrodes and instrumentation defects are a few
sources of error.
We therefore recommend determining the recovery rate
of water at regular intervals. Such a control determination
is relatively simple: 1 g (exactly weighed by difference) of
Hydranal-Water Standard 0.1 or 1.0 is injected into the
titration cell using a calibrated syringe to determine the
water content. Recovery rates for water of 0.03 mg H O/g2
for Hydranal-Water Standard 1.0 or 0.005 mg H O/g for2
Hydranal-Water Standard 0.1 from the value given on the
certificate can be considered acceptable. Such a control
titration can be carried out following a series of water
determinations. It should be conducted if the reagent or
equipment appears suspect. A daily control will give the
analyst additional assurance.
5.3.7 Replacement of the reagents
The spent reagent can be replaced relatively easy. The spent
anoly te is removed from the anodic compartment through
the sample port opening by means of a plastic suction
bottle (section 6.5). Certain instruments are equipped
with pumps. The anodic compartment is subsequently re-
as described in section 5.3.1. The cathodic compar tment is
similarly replenished with Hydranal-Coulomat CG (section
5.3.2). It is common practice to replenish both reagents at
the same time.
Changing the reagent in a diaphragm-less cell is relatively
easy. After the spent reagent is removed, fresh Hydranal-
Coulomat A /AG/E /AG-H/AG-Oven is added to the cell.
Determining whether or not the reagent is spent and
requires changing is more complicated. There are many
factors that influence this decision, including:
• If the drif t or background is significantly increased
• If the titration cell is full
• If the water capacit y of the reagent has
been exhausted
• If the instrument is defective
Usually, it is a full titration cell that causes the replacement
of the reagent. Most cells have a 100 mL reagent capacity
and a total cell volume of 150-160 mL. The reagent
must be replenished after 50-60 mL of sample has been
added. Furthermore, the successive dilution reduces the
conductivit y and necessitates replenishment of the reagent.
together with the known equation for the KF reaction

18
ensures a total capacity of 1000 mg H O per 100 mL2
volume. This water capacit y can be fully utilized. Hydranal-
Coulomat Oil has a water capacity of 300 mg per 100 mL.
The capacity limit of the catholyte cannot be calculated
because exchange reactions take place with the anode. It
must be determined empirically. The water capacit y of 5 mL
Hydranal-Coulomat CG is 200-300 mg. Gases develop
when approximately 200 mg H O are analyzed. They do2
not however influence the function of the catholyte. A
dissipation of sulfur can take place when more than 30 0 mg
H O is determined per 5 mL of catholyte. This is avoided by2
replenishing the reagent early.
A calculation of the total amount of water is relatively
dif ficult as not only the water from the sample, but also the
blank consumption of reagent during the self-drying time
must be considered. Certain instruments are equipped
to register the total water consumption since the last 1. Hydranal-Methanol dry is added to the titration
replacement of the reagent. This enables an accurate
calculation of the remaining capacit y of the reagent.
A drif t increase of ten means the reagent must be replaced.
An increase in the drift can have different causes. Side
reactions, such as esterification or the formation of ketals
lead to a production of water. A continual infiltration of
moisture into the cell can also be the source. However, a
spent catholyte solution is most often the cause. When
reductive substances from the cathodic compartment
diffuse through the diaphragm into the anodic
compartment, they react like water and cause an increase
in the drift. A drift increase can equally be caused by the
diffusion of moisture from the cathodic into the anodic
compartment. Whatever the cause, it is recommended to
replenish the reagent in order to guarantee an accurate
and error-free water determination.
In case of doubt, the recovery rate of water should be
determined as described in section 5.3.6. This method is
a reliable way of determining whether the equipment is
functioning properly and capable of producing accept-
able results.
5.3.8 Machine always switched on
The coulometric cell should always be dr y and operational
to enable a fast water determination. This can be achieved
if the machine remains permanently switched on. Moisture
penetrating the cell will be immediately eliminated this way.
No additional reagent is consumed by using this working
method since the amount of reagent used is determined
by the amount of free moisture. If the machine is switched
off, the same amount of water collects in the cell and
will be eliminated only when the machine is switched on,
which can take a long time and uses up the same amount
of reagent.
5.4 Coulometry without a diaphragm
For cells without a diaphragm, Hydranal-Coulomat AD/E/
AG/AG-Oven is used. The same principle as described in
section 5.3 applies to carr ying out this form of coulometr y. A
catholy te is not necessar y, so section 5.3.2 is not applicable.
5.5 Back titrations
The back titration method was used more often in
the past. This method was of significance when the
KF reagents contained pyridine and were thus slow. The
determination of water could be accelerated using the back
titration technique.
Titrations with Hydranal reagents are rapid and back
titrations are not usually necessary. The need to perform
a back titration with Hydranal reagents is rare [1], although
it is possible in principle with all one- and two-component
Hydranal reagents. The individual steps are as follows:
cell and titrated to dryness using Hydranal-
Composite according to section 5.1.3. If the two-
component reagent is used, Hydranal-Solvent
is added to the cell and dried using Hydranal-
Titrant according to section 5.2.3. The working
medium can be modified through the addition of
other solvents.
2. The sample is then weighed into the cell according to
the procedure outlined in section 5.1.4 or 5.2.4.
3. An excess of titrant is added, e.g. 10 mL of Hydranal-
Composite or Hydranal-Titrant. The quantity of titrant
is calculated to ensure that the expected water content
is exceeded.
4. Af ter waiting for a time determined by the sample being
investigated, the working medium is back titrated with
Hydranal-Water-in-methanol 5.0.
The water content of the sample is calculated from the
difference between the water capacity of the added
titrant and the water content of the methanol used for the
back titration:
mg H O = ( WE2 KF
x mLKF
) - ( WEmeth.
x mLmeth.
)
For back titration, t wo solutions of known titer are required:
the KF solution and the Hydranal-Water-in-methanol 5.0.
The titer of the KF solution is determined according to
the procedure in section 5.6. The titer of the Hydranal-
Water-in-methanol 5.0 is determined against the adjusted
KF solution.
5.6 Standardization of titer
Determining the titer of reagents is par t of the routine work in
a KF laborator y. It is a necessar y task as the titer of standard
solutions changes or can change by the penetration of
atmospheric moisture [1]. The frequency of the titer control
depends mainly on the choice of the titrating agent employed
and how tightly sealed the equipment is against permeation
by atmospheric moisture.

19
The stability of the titer of Hydranal-Composite is
exceptionally good and a weekly control of its titer
is suf ficient.
The determination of the titer of Hydranal-Titrant is really
not necessary since it can be stored indefinitely. The titer
should, however, be controlled occasionally. This apparent
contradiction arises from the hygroscopic nature of absolute Sodium tartrate dihydrate is mentioned in some
methanol. Improper handling of the titrant can lead to
infiltration of atmospheric moisture and a decrease in the
titer of the reagent for subsequent titrations.
The titer is calculated as the water equivalent, WE (in
mg H O per mL of reagent) for Karl Fischer titrations:2
weight of water in mg
consumption of reagent in mL
We prefer to frequently control the titer, which we consider
to be more a control of the titration conditions. The titer of
Hydranal-Composite changes approximately 0.01 water
equivalent per week. Such changes are hardly significant
for a daily control of the titer. If, however, large deviations
are detected the titration conditions must be inspected.
Titer fluctuations can arise from the infiltration of moisture,
the equipment being no longer air-tight, spent drying agent
and other causes. Titer values that fluctuate from day to day,
increasing and decreasing, are a proven indication of scatter
in the analysis and are not due to a fluctuation of the titer.
We do not recommend determining the titer in the morning,
even though it is a common practice. Because the plastic
tubing on the instruments is permeable to moisture, the
titer of the KF reagent typically decreases slightly during
the night. The tubes should be flushed several times with
fresh reagent prior to determining the titer. The determined
titer must always be compared with the previous day’s
results to ensure it does not vary in value outside the
normal, expected range.
A fluctuation in the room temperature of the laboratory
can cause fluctuations in the titer. KF reagents consist of
organic solvents whose coefficients of thermal expansion
are significantly greater than that of water. A temperature
increase of 1°C will usually result in a titer decrease of
a b o u t 0 . 1% .
The titer is determined in the same manner as described
in sections 4.1 and 4.2. Instead of titrating the water in a
sample, a substance of known water content or a known
amount of water is added and titrated. The same working
conditions, i.e. the same solvent(s), the same volumes
and the same temperature are used as for the subsequent
investigation of the sample.
Different standards offer advantages and limitations and
are used for the titer determination [1]. For volumetry
we recommend the use of Hydranal-Standard Sodium
Tartrate Dihydrate for an exact titer determination or
Hydranal-Water Standard 10.0 which is a liquid standard
in sealed glass ampoules. The use of pure water is equally
acceptable, however the low amounts required are dif ficult
to handle and weigh.
5.6.1 HYDRANAL-Standard Sodium
Tartrate Dihydrate
regulations as the primar y water standard for KF titrations.
It remains stable, does not effloresce (which means to
become a powder by losing water of crystallization) and is
not hygroscopic under normal laborator y conditions.
Hydranal Sodium Tar trate Dihydrate is available in dif ferent
qualities like “pure chemical”, “normal standard” or “CRM
standard”. It has a water content of approx. 15.66%. The
exact value is stated on the Repor t of Analysis or Cer tificate
of Analysis provided with these different qualities. It
dissolves relatively quickly but only in limited amounts in
pure methanol. By using Hydranal-Solvent or a mixture
of Hydranal-Solvent and methanol, the solubility can be
increased to a certain extent. Depending on the titer to be
determined, a size of 0.1-0.5 g (equal to 15-75 mg H2O)
is used. The consumption of titrating reagent to be
standardized should be about half of burette volume.
5.6.2 HYDRANAL-Water Standard 10.0
This standard is a liquid standard for volumetric water
determinations. It is each delivered in 8 mL glass ampoules.
One package contains 10 ampoules and a Report of
Analysis giving the exact water content for the batch. To
determine the titer, an ampoule is opened and portions of
about 2 g (exactly weighed by difference) are added to the
titration vessel using a syringe.
5.6.3 Water
Pure water can also be used as a standard calibration
substance. This would appear to be the simplest method.
However, it is not trivial to accurately weigh and add
precisely 20-50 mg of water. Weighing by difference of a
micro-syringe proves to be the most suitable method.
5.7 End point indication
All of the customary methods of KF end point indication
can be employed when using Hydranal reagents. This
is also valid for the preferred biamperometric and
bipotentiometric methods [1], as well as for the seldom-
used method of visual indication. The indication of the
end point is improved by the use of Hydranal reagents no
matter which method of end point indication is used.
5.7.1 Electrometric indication
The antiquated KF reagents containing pyridine were
notorious for how dif ficult it was to determine the end point
of a titration. The equivalency point of the reaction was
reached slowly with these reagents, primarily due to the
WE =

20
weak basicity of pyridine. Actual reversal of the end point
was not uncommon.
To obtain unambiguous end point determination, a special
technique was developed. The end point was established
when a defined potential (bipotentiometric indication), or
current (biamperometric indication) was not only reached
but remained constant for a specified length of time, e.g. 20
seconds. This end point delay is typical of the KF titration
and all the instruments available incorporate an end point
duration setting, which can be adjusted individually (see
section 6.6). A duration or delay setting of twenty seconds
has proven to be preferred time in practice. Changing this
delay time often changes the consumption of KF solution
and thus alters the results.
The latest development for end point determination is the
“drift-stop”. Using this method, the titration is stopped
when a chosen drif t is measured in the titration cell.
Special protocols for end point determination are not
necessary when using Hydranal reagents. A stable end
point is reached (see section 3) quickly. The delay time can
be adjusted according to the substance under investigation.
The delay time can be reduced to five seconds if only the
adherent moisture is being determined. This also applies
to titrations where the influence of side reactions should
be suppressed. If, on the other hand, the water in the sample
can be released and titrated only slowly, the end point delay
time can be set to 60 seconds in order to ensure a complete
determination of the total amount of water present. There
is no influence on the titration result in either case; the titer
remains constant independent of the titration conditions.
5.7.2 Visual indication
Conventional KF reagents yield a color change from yellow
to brown that is relatively vague. A sulfur dioxide-iodide
complex [SO2I]⁻ is present in the system at a pH of 4-5 just
before the equivalence point is reached and causes the
yellow coloration.
This complex dissociates at pH values of 6-7 and the
titration solution becomes colorless. Since Hydranal
reagents have a higher pH than conventional reagents,
there is less yellow coloration and the color change to
brown is easier to recognize. A complete decolorization of
the working medium can be achieved by the addition of
Hydranal-Buffer for Acids. The pH of the system is raised
to 6-7 and the solution becomes completely colorless.
In practice, a sufficient (5 mL), amount of Hydranal-
Buffer for Acids is added to the working medium prior to
the pre-titration. The titration is then carried out in the
normal manner. Refer to sections 4.1.3 and 4.2.3 for the
appropriate procedures.
5.7.3 Photometric indication
Use of photometric methods to measure the end point is
currently used only in flow injection methods of analysis.
Wavelengths of 525 or 600 nm are monitored. The
absorption spectrum of Hydranal reagents is depicted in
Figure 5.7.3. Curve A shows the absorption spectrum with
an excess of iodine; curve B with an excess of water. The
greatest sensitivity is achieved in the 460-480 nm range.
If the excess iodine is to be measured, the less sensitive
range (520-620 nm) is chosen.
Figure 5.7.3. Absorption spectrum of Hydranal
reagents: A - with an excess of iodine; B - with an
excess of water.
B A
500
E
[nm]
1.0
0.6
0.2
400 600 700

21
Successful Karl Fischer titration requires techniques 6.3 Titration cells
and considerations beyond those of normal volumetric
titrations because of the acute need to prevent
contamination of the system by extraneous moisture. In
this section, we will discuss certain details that demand
par ticularly close attention.
6.1 The KF laboratory
Karl Fischer titrations do not require a specialized
laboratory. When using Hydranal reagents a fume hood is
not required because these reagent s do not contain pyridine
and do not possess a noxious odor. A KF titration should
be carried out under normal ambient conditions whenever
possible. Room temperature higher than normal should
be avoided since the organic solvents, such as methanol
or diethylene glycol monoethyl ether, have relatively low
thermal expansion coefficients (approximately 0.1%
per °C). Temperature fluctuations can influence the titer
significantly. Fur thermore, equipment such as water baths,
which can increase the relative humidit y of the atmosphere,
should not be placed in the vicinit y of KF instrumentation.
6.2 Titration instrumentation
Many different titration instruments are used for KF
titration. Commercially available equipment is preferred.
These instruments are available from a variety of
manufacturers worldwide. There is a wide range of options
from simple to complex. Simple instruments consist of a
burette and an indication system. Titrators carry out the
titration automatically, register the weight of the sample
being determined, adapt the titration rate to the amount of
water in the sample and print out the titration results [1].
Simple titration apparatus are also available that enable KF
titrations to be carried out with minimum equipment and
at minimum cost [1]. These systems are desirable when
KF titrations are performed only occasionally or when
investigating the potential for the method before investing
in more expensive equipment.
Hydranal reagents are suited for all types of KF
instrumentation. We have tested and/or used equipment
from Metrohm, Mettler- Toledo, SI Analytics, Radiometer,
Orion, Prolabo, Fisher Scientific, Photovolt, Mitsubishi,
Hiranuma, Kyoto Electronic and CSC Scientific. We use
many of these instruments in our Hydranal laboratories to
ensure compatibilit y of our methods.
The different KF titration instruments differ in their design
and concept, their ease of use and handling. It is not
possible to give detailed instructions on the specifics of
each instrument. Instead, we will mention a few basic rules
that we consider to be important for ever yday practice and
are common to all t ypes of instruments.
Commercially available volumetric titration cell s are usually
glass vessels kept tightly closed by plastic seals. The
penetration of atmospheric moisture is kept to a minimum.
The cell is hermetically sealed when in use, and is only
briefly opened in order to add the sample or to replenish the
solvent. When titration cells are disassembled, the residual
adherent solvent adsorbs atmospheric moisture making
the subsequent titration of the re-assembled titration cell
ver y dif ficult. When this happens, a complete overhaul and
dr ying of the cell is required. Best results are achieved by a
thorough, final rinse with methanol or other water-miscible
solvent following the removal of solids. The cell is then
dried with a dr yer, or in a dr ying cabinet at 50-70°C.
The size of the titration cell should not be larger than
absolutely necessary because the unused volume is a
source of extraneous moisture. The inner surfaces of the
cell should be smooth, enabling a uniformly thin film of
methanol. Any surface defects where methanol can collect
will retain water and cause sluggish end points. Corners
and seals that enable the formation of pockets of solvent
are particularly detrimental. Titration cells should be gas-
tight to allow venting with dried air.
Titrations demanding high accuracy, like coulometric
titrations, should be carried out only in glass titration cells.
Titration cells with plastic seals have a higher permeabilit y
for water vapor. We determined the permeation rate
being as high as 1 mg H O/hour into titration cell of such2
construction. This is equivalent to a reagent consumption
rate of 0.003 mL/min. Corresponding consumption rates
for titration cells constructed completely from glass are
much lower, approximately 0.05 mg H O/hour.2
In our Hydranal laboratories and other facilities that
use KF titration, we use titration apparatus with ground
glass connections for titrations requiring high accuracy.
Such apparatus can be easily dried by the customary
pre-titration. Commercially available titration cells are
preferred for routine work as these provide acceptable
accuracy and are ver y practical.
Even glass titration cells are not absolutely impermeable
to water vapor. They will absorb moisture from the
atmosphere when left unused. This causes sluggish end
points in subsequent titrations. It is recommended to keep
the equipment programmed to a continuous overnight
titration in order to prevent an accumulation of moisture
in the cell when not in use. The same effectiveness can
be achieved by the addition of a sufficient amount of
titration agent to the cell. The cell should then be shaken
the next day to remove the moisture in any solvent pockets
and adherent on the cell walls. This procedure is strongly
recommended for coulometric titration cells.
HYDRANAL Manual Chapter 6: Laboratory recommendations
Chapter 6. Laboratory recommendations

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